The term "waxing" is used herein to indicate that the invention is particularly applicable to the case where the liquid to be treated includes certain components that may indeed be miscible, e.g. paraffins in diesel oil, but which tend to solidify first when the temperature drops and which can then give rise to localized blockages in a circuit having other portions in which the liquid remains sufficiently fluid. Nevertheless, the invention is also applicable to a liquid in which solidification takes place at a single determined temperature and then takes place completely.
The invention is even more particularly suitabIe for vehicles, in particular goods vehicles, having a diesel engine running on diesel oil. The circuit for feeding the engine with fuel from the tank in a common type of goods vehicle includes the following items:
a feed pump having moderate delivery pressure for transferring diesel oil from the tank; PA1 a static centrifugal separator for intercepting water droplets and solid particles that may be contained in the diesel oil; PA1 filters for intercepting other solid particles of various sizes, e.g. a prefilter for intercepting large particles and a fine filter for intercepting finer particles; and PA1 an injection pump for injecting appropriate volumes of diesel oil at appropriate instants into each engine cylinder. PA1 a separator for a liquid capable of waxing, in particular for diesel fuel, the separator comprising: PA1 a separation bowl having an axis and a bowl opening around said axis; PA1 a lid for closing said bowl opening, said lid being constituted at least in part by a heat-conducting material and having an inside face adjacent to said separation bowl and an opposite outside face; PA1 a filtering wall extending around the said axis inside said separation bowl, said wall being carried by said lid from said inside face thereof; PA1 a separator inlet for receiving a liquid to be treated, the liquid containing elements capable of waxing under the effect of low temperature, said inlet conveying said liquid to face an upstream face of said filtering wall; PA1 a separator outlet for receiving said liquid to be treated after it has passed through said filtering wall to face a downstream face thereof; and PA1 a heater element in thermal contact with said lid for heating said liquid to be treated via said lid. PA1 reducing the cost and/or bulk of the separator; PA1 providing more effective and/or better distributed heating of the diesel oil in the separator; and/or PA1 minimizing the risks of the heater element situated in such a separator being damaged, in particular during maintenance operations such as changing the filter element. PA1 said heat-conveying extension forms fins which extend radially and axially and which are angularly distributed around said axis; PA1 said lid is generally in the form of a thick plate perpendicular to said axis, inlet and outlet ducts being formed parallel to said plate in the thickness thereof respectively for conveying said liquid to be treated from said separator inlet to said filtering wall, and from said filtering wall to said separator outlet; PA1 said filtering wall and said separation bowl are disposed beneath said lid, said lid including the following in successive levels from bottom to top: said heat-conveying extension, said extension surrounding said filtering wall; PA1 a heating level including said heater elements, said element being elongate and forming substantially one turn around said axis; and PA1 a connection level in which said inlet and outlet ducts are formed; PA1 the separator further includes a thermostat placed in thermal contact with said lid and controlling said heater element to maintain the temperature of said lid between predetermined limits; PA1 said heater elements is an electrical heater resistance; and PA1 said heater resistance is incorporated in the mass of said lid by casting, said lid being constituted by a metal having a melting point which is substantially lower than that of the materials constituting said resistance. The additional cost due to incorporating the resistance in this way is very small because the conventional and cheap way of making the lid is by casting.
A filter element may be integrated in the centrifugal separator.
Such a goods vehicle may sometimes be required to start and run when the temperature of the atmosphere is low enough to solidify paraffins contained in the diesel oil. That is why a major need has long been felt to avoid particles of solidified paraffin blocking the narrow passages formed for diesel oil through the separator in cold weather. Such narrow passages are constituted, in particular, by the pores through the filter element which may be integrated in the separator.
A known solution to the problem posed by this need consists in adding additives to the diesel oil to delay the formation and the growth of particles of solidified paraffin.
Another solution appears in a first prior separator which does not include centrifugal separation means. A separator of the present invention includes some items in common with said prior separator with respect to the functions mentioned below. These common items are:
Such a prior separator is described in Document DE-A-2 845 519 (a German patent application no. by Bosch). In this prior separator, the separation bowl is constituted by a filter capsule, said lid is generally in the form of a thick plate, and said inlet duct extends through the thickness of said plate as does a hot water circuit which constitutes said heater element. This first prior separator suffers, in particular, from the drawback of being poor at separating out some impurities such as water droplets and of requiring the filter element to be replaced too frequently.
A second prior separator includes a fixed centrifuging deflector disposed in said separation bowl, which then constitutes a centrifuging bowl. It was manufactured by the American firm Racor Industries Inc., of Modesto, California USA. It is derived from a separator as described in U.S. Pat. No. 3 931 011 (Richards et al.) to which said heater element has been added in the form of an electrical resistance. This resistance is immersed in the centrifuged diesel oil flowing inside an enclosure which is formed above the lid of the centrifuging bowl and which contains a filter element over said resistance. Given the direction of liquid flow, the resistance is thus placed upstream from said filter element and it is temporarily exposed at the end of the enclosure each time the filter element is changed after it has become clogged.
This second prior filter operates in a generally acceptable manner but its users would prefer it to be cheaper to purchase, more compact, and easier to maintain without risk of damage. Naturally, it is also desirable to minimize the amount of electrical energy which is consumed for initially heating diesel oil in cold weather.
The present Applicant has obtained a French patent No. 2 596 668 for a centrifugal separator which does not include a heater element.